This invention relates generally to a system for logging earth boreholes and specifically to a system which utilizes means to assist a well logging instrument to traverse highly deviated earth boreholes.
It has become relatively common within the last few years to drill wells in the search for oil and gas and the like with a portion of the bore deviating from the usual vertical orientation thereof. The deviation or inclination may extend for a considerable distance at angles ranging to 70.degree., sometimes returning to the usual vertical orientation. In some instances, such boreholes might even extend past 90.degree. from the vertical and actually be extending in the "up" direction for some distance.
It is also well known in the art of drilling such wells to attempt the logging of the formations surrounding such boreholes with logging instruments run into the well bore on a wireline and/or cable to perform various operations. Such tools usually depend upon the force of gravity to permit positioning of the well tools at the desired formation in the well bore.
Manifestly, the relatively horizontal angle of the deviated portion of the well bore will not permit the wireline-actuated tools to move into the lower portion of the well bore since the friction of the well tool in the deviated portion works against the force of gravity. Thus, it has become essential to provide some means of causing the well logging instrument to pass through the deviated portions of the well bore.
Another problem associated with such boreholes relates to the instability of some formations penetrated by the well bore, thus causing borehole diameter changes, some very abrupt. Ledges are formed, and the logging instrument lodges against them.
Furthermore, although there have been attempts in the prior art to pump logging instruments down the borehole, instruments have generally suffered from the problems associated with having a wireline attached to the instrument, or because of having no correlation between the well logging signals and the true depth in the borehole.
Still another problem associated with attempting to use so-called pumpdown instruments relates to the fact that once the instrument is pumped out the end of the drill pipe, it again is subject to the same problems associated with deviated boreholes, namely, that of having ledges and abrupt changes in the direction of the borehole. Associated with this problem, as one attempts to use tubular extensions outside the end of the drill pipe, the wireline gets in the way of attempting to join the tubular sections together.
It is therefore the primary object of the present invention to provide a new and improved method and apparatus for logging earth boreholes;
It is also an object of the present invention to provide new and improved method and apparatus for logging highly deviated earth boreholes which allow such instruments for the logging of such earth boreholes to utilize wirelines connected to the earth's surface.
The objects of the invention are accomplished, generally, by a tubular extension apparatus having a well logging instrument positioned at one end and adapted to be lowered through the drill pipe and electrical connection means attached to the wireline cable which can be lowered through the tubular extension to make a gravity contact with the well logging instrument so that electrical communication can be maintained between the instrument and the earth's surface. The well logging instrument and tubular extension can then be lowered through the drill pipe and out the lower end of the drill pipe to thereby place the logging instrument into position at a desired location within the earth formation beneath the lower end of the drill pipe.